#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(m), b(m); REP(i, m) cin >> a[i] >> b[i], --a[i], --b[i];
  vector<int> towns(m * 2 + 2, 0);
  copy(ALL(a), towns.begin());
  copy(ALL(b), towns.begin() + m);
  towns.back() = n - 1;
  sort(ALL(towns));
  towns.erase(unique(ALL(towns)), towns.end());
  const int l = towns.size();
  vector<vector<int>> graph(l);
  REP(i, m) graph[lower_bound(ALL(towns), a[i]) - towns.begin()].emplace_back(lower_bound(ALL(towns), b[i]) - towns.begin());
  vector<int> dp(l, numeric_limits<int>::max());
  dp[0] = 0;
  REP(i, l - 1) {
    chmin(dp[i + 1], dp[i] + (towns[i + 1] - towns[i]) * 2);
    for (int j : graph[i]) chmin(dp[j], dp[i] + (towns[j] - towns[i]) * 2 - 1);
  }
  cout << dp[l - 1] << '\n';
  return 0;
}